Loyalist Shiban Khan and his Brotherhood of the Storm managed to eventually board the Swordstorm via Jetbikes thanks to the efforts of Departmento Munitorum official Ilya Ravallion, who opened a docking bay for them. Shiban led his forces to the Swordstorm's bridge, battling Torghun's Brotherhood of the Moon. Around the same time a fleet of four Death GuardBattleships led by Mortarion himself aboard the Endurance arrived in the Prospero system. As the Death Guard fleet waited to see which way the White Scars would turn, Mortarion teleported to Prospero's surface and attempted to turn the Great Khan himself. When Mortarion failed, the two Primarch's and their retinues came to blows. Meanwhile Shiban's efforts on the Swordstorm's bridge were strengthened when Jemulan Noyan-Khan arrived and fought against the conspirators. Loyalists began regaining control of the White Scars fleet, as Targutai Yesugei arrived and had his small fleet of captured traitor ships manned by Salamanders and Iron Hands engage the Death Guards.[1]

The battle in space caused Mortarion to leave the Khan, knowing his mission had been a failure. Jaghatai was teleported aboard the Swordstorm shortly after, arriving amidst a bloody melee between his own Legion. The Great Khan's arrival promptly ended the fight, and most of the traitor surrendered themselves. He then directed his fleet to engage the Death Guard, causing a brief but intense battle that saw Mortarion withdraw. As the White Scars pursued, the Death Guard conducted a spiteful purge of the planets surrounding Prospero.[1]